1. Field of the Invention
The present invention relates to a drive apparatus and a drive method for an electromagnetic drive type actuator.
2. Description of the Related Art
There is known an electromagnetic drive type actuator having: a movable element; a fixed element; a connection element connecting these elements; a magnetic field generation element fixed to one of the fixed element and the movable element; and a drive coil fixed to the other one of the fixed element and the movable element. This type of electromagnetic drive actuator is driven by supplying a pulsed current to the drive coil, for example, so that the movable element is oscillated with respect to the fixed element in the resonance state by the force acting between the drive coil and the magnetic field generation element.
Some of the electromagnetic drive type actuators have an oscillation detection sensor for detecting a deflection angle or a deflection angular velocity of the movable element for the further accurate control, but some do not have such an oscillation detection sensor to get a large deflection angle or reduce the size.
In drive apparatuses for the electromagnetic drive type actuator having no oscillation detection sensor, some can detect a deflection angle or a deflection angular velocity of the movable element based on the voltage between the both ends of the drive coil. Jpn. Pat. Appln. KOKAI publication No. 10-207973 entitled “drive circuit for vibration mirror type scanning apparatus” discloses a conventional example of such a drive apparatus.
This drive apparatus subjects the actuator to resonance drive by applying a pulsed drive signal to a vibration mirror drive coil (VM coil). Further, this drive apparatus detects the voltage between the both ends of the vibration mirror drive coil by a voltage sampler, and raises the pulsed drive signal with a timing at which the detection voltage becomes zero. Furthermore, the pulse width is determined by comparing a peak value of the detection voltage of the voltage sampler with a target voltage.
It is good enough to match rising of the pulsed rive current with the peak of the angular velocity for the efficient drive of the electromagnetic drive actuator. However, the above-described prior art drive apparatus raises the pulsed drive signal with the timing at which the detection voltage of the voltage sampler becomes zero. That is, rising of the pulsed drive current is matched with the timing at which the angular velocity of the vibration mirror becomes zero. Therefore, the drive apparatus in the prior art can not perform the efficient drive.
The drive apparatus in the prior art uses a peak value of the detection voltage as amplitude information. Since the peak value of the detection voltage is readily affected by the disturbance such as noises, there is a doubt in validity of the amplitude information.
The drive apparatus in the prior art adjusts the deflection angle amplitude by changing a pulse width of the drive current. Therefore, the distortion of a signal when eliminating the drive signal overlapped on the detection voltage is increased/decreased in dependence upon the pulse width. Therefore, it is hard for the drive apparatus in the prior art to perform accurate amplitude detection. Furthermore, since the deflection angle amplitude is adjusted by changing the pulse width of the drive current, the pulse width must be less than ¼ of a vibration cycle of the actuator. That is, there is limit in the amplitude adjustment range.